/*
 * Routines to compress and uncompess tcp packets (for transmission
 * over low speed serial lines.
 *
 * Copyright (c) 1989 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
 *	- Initial distribution.
 *
 * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
 * so that the entire packet being decompressed doesn't have
 * to be in contiguous memory (just the compressed header).
 *
 * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
 * for a 16 bit processor.
 */

#include <string.h>

#include "ppp.h"
#include "vj.h"
#include "pppdebug.h"

#if VJ_SUPPORT > 0

#if LINK_STATS
#define INCR(counter) ++comp->stats.counter
#else
#define INCR(counter)
#endif

#if defined(NO_CHAR_BITFIELDS)
#define getip_hl(base)	((base).ip_hl_v&0xf)
#define getth_off(base)	(((base).th_x2_off&0xf0)>>4)
#else
#define getip_hl(base)	((base).ip_hl)
#define getth_off(base)	((base).th_off)
#endif

void vj_compress_init(struct vjcompress *comp)
{
        register u_int i;
        register struct cstate *tstate = comp->tstate;

#if MAX_SLOTS == 0
        memset((char *)comp, 0, sizeof(*comp));
#endif
        comp->maxSlotIndex = MAX_SLOTS - 1;
        comp->compressSlot = 0;		/* Disable slot ID compression by default. */
        for (i = MAX_SLOTS - 1; i > 0; --i)
        {
                tstate[i].cs_id = i;
                tstate[i].cs_next = &tstate[i - 1];
        }
        tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
        tstate[0].cs_id = 0;
        comp->last_cs = &tstate[0];
        comp->last_recv = 255;
        comp->last_xmit = 255;
        comp->flags = VJF_TOSS;
}


/* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
 * checks for zero (since zero has to be encoded in the long, 3 byte
 * form).
 */
#define ENCODE(n) { \
	if ((u_short)(n) >= 256) { \
		*cp++ = 0; \
		cp[1] = (n); \
		cp[0] = (n) >> 8; \
		cp += 2; \
	} else { \
		*cp++ = (n); \
	} \
}
#define ENCODEZ(n) { \
	if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
		*cp++ = 0; \
		cp[1] = (n); \
		cp[0] = (n) >> 8; \
		cp += 2; \
	} else { \
		*cp++ = (n); \
	} \
}

#define DECODEL(f) { \
	if (*cp == 0) {\
		u32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
		(f) = htonl(tmp); \
		cp += 3; \
	} else { \
		u32_t tmp = ntohl(f) + (u32_t)*cp++; \
		(f) = htonl(tmp); \
	} \
}

#define DECODES(f) { \
	if (*cp == 0) {\
		u_short tmp = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
		(f) = htons(tmp); \
		cp += 3; \
	} else { \
		u_short tmp = ntohs(f) + (u_short)*cp++; \
		(f) = htons(tmp); \
	} \
}

#define DECODEU(f) { \
	if (*cp == 0) {\
		(f) = htons(((u_short)cp[1] << 8) | cp[2]); \
		cp += 3; \
	} else { \
		(f) = htons((u_short)*cp++); \
	} \
}

/*
 * vj_compress_tcp - Attempt to do Van Jacobsen header compression on a
 * packet.  This assumes that nb and comp are not null and that the first
 * buffer of the chain contains a valid IP header.
 * Return the VJ type code indicating whether or not the packet was
 * compressed.
 */
u_int vj_compress_tcp(
        struct vjcompress *comp,
        struct pbuf *pb
)
{
        register struct ip *ip = (struct ip *)pb->payload;
        register struct cstate *cs = comp->last_cs->cs_next;
        register u_short hlen = getip_hl(*ip);
        register struct tcphdr *oth;
        register struct tcphdr *th;
        register u_short deltaS, deltaA;
        register u_long deltaL;
        register u_int changes = 0;
        u_char new_seq[16];
        register u_char *cp = new_seq;

        /*
         * Check that the packet is IP proto TCP.
         */
        if (ip->ip_p != IPPROTO_TCP)
                return (TYPE_IP);

        /*
         * Bail if this is an IP fragment or if the TCP packet isn't
         * `compressible' (i.e., ACK isn't set or some other control bit is
         * set). 
         */
        if ((ip->ip_off & htons(0x3fff)) || pb->tot_len < 40)
                return (TYPE_IP);
        th = (struct tcphdr *)&((long *)ip)[hlen];
        if ((th->th_flags & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK)
                return (TYPE_IP);

        /*
         * Packet is compressible -- we're going to send either a
         * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
         * to locate (or create) the connection state.  Special case the
         * most recently used connection since it's most likely to be used
         * again & we don't have to do any reordering if it's used.
         */
        INCR(vjs_packets);
        if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr
                        || ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr
                        || *(long *)th != ((long *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
        {
                /*
                 * Wasn't the first -- search for it.
                 *
                 * States are kept in a circularly linked list with
                 * last_cs pointing to the end of the list.  The
                 * list is kept in lru order by moving a state to the
                 * head of the list whenever it is referenced.  Since
                 * the list is short and, empirically, the connection
                 * we want is almost always near the front, we locate
                 * states via linear search.  If we don't find a state
                 * for the datagram, the oldest state is (re-)used.
                 */
                register struct cstate *lcs;
                register struct cstate *lastcs = comp->last_cs;

                do {
                        lcs = cs;
                        cs = cs->cs_next;
                        INCR(vjs_searches);
                        if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
                                        && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
                                        && *(long *)th == ((long *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
                                goto found;
                } while (cs != lastcs);

                /*
                 * Didn't find it -- re-use oldest cstate.  Send an
                 * uncompressed packet that tells the other side what
                 * connection number we're using for this conversation.
                 * Note that since the state list is circular, the oldest
                 * state points to the newest and we only need to set
                 * last_cs to update the lru linkage.
                 */
                INCR(vjs_misses);
                comp->last_cs = lcs;
                hlen += getth_off(*th);
                hlen <<= 2;
                /* Check that the IP/TCP headers are contained in the first buffer. */
                if (hlen > pb->len)
                        return (TYPE_IP);
                goto uncompressed;

found:
                /*
                 * Found it -- move to the front on the connection list.
                 */
                if (cs == lastcs)
                        comp->last_cs = lcs;
                else {
                        lcs->cs_next = cs->cs_next;
                        cs->cs_next = lastcs->cs_next;
                        lastcs->cs_next = cs;
                }
        }

        oth = (struct tcphdr *)&((long *)&cs->cs_ip)[hlen];
        deltaS = hlen;
        hlen += getth_off(*th);
        hlen <<= 2;
        /* Check that the IP/TCP headers are contained in the first buffer. */
        if (hlen > pb->len)
        {
                PPPDEBUG((LOG_INFO, "vj_compress_tcp: header len %d spans buffers\n",
                          hlen));
                return (TYPE_IP);
        }

        /*
         * Make sure that only what we expect to change changed. The first
         * line of the `if' checks the IP protocol version, header length &
         * type of service.  The 2nd line checks the "Don't fragment" bit.
         * The 3rd line checks the time-to-live and protocol (the protocol
         * check is unnecessary but costless).  The 4th line checks the TCP
         * header length.  The 5th line checks IP options, if any.  The 6th
         * line checks TCP options, if any.  If any of these things are
         * different between the previous & current datagram, we send the
         * current datagram `uncompressed'.
         */
        if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0]
                        || ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3]
                        || ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4]
                        || getth_off(*th) != getth_off(*oth)
                        || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2))
                        || (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*th) - 5) << 2)))
                goto uncompressed;

        /*
         * Figure out which of the changing fields changed.  The
         * receiver expects changes in the order: urgent, window,
         * ack, seq (the order minimizes the number of temporaries
         * needed in this section of code).
         */
        if (th->th_flags & TCP_URG)
        {
                deltaS = ntohs(th->th_urp);
                ENCODEZ(deltaS);
                changes |= NEW_U;
        } else if (th->th_urp != oth->th_urp)
                /* argh! URG not set but urp changed -- a sensible
                 * implementation should never do this but RFC793
                 * doesn't prohibit the change so we have to deal
                 * with it. */
                goto uncompressed;

        if ((deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) != 0)
        {
                ENCODE(deltaS);
                changes |= NEW_W;
        }

        if ((deltaL = ntohl(th->th_ack) - ntohl(oth->th_ack)) != 0)
        {
                if (deltaL > 0xffff)
                        goto uncompressed;
                deltaA = (u_short)deltaL;
                ENCODE(deltaA);
                changes |= NEW_A;
        }

        if ((deltaL = ntohl(th->th_seq) - ntohl(oth->th_seq)) != 0)
        {
                if (deltaL > 0xffff)
                        goto uncompressed;
                deltaS = (u_short)deltaL;
                ENCODE(deltaS);
                changes |= NEW_S;
        }

        switch (changes)
        {

        case 0:
                /*
                 * Nothing changed. If this packet contains data and the
                 * last one didn't, this is probably a data packet following
                 * an ack (normal on an interactive connection) and we send
                 * it compressed.  Otherwise it's probably a retransmit,
                 * retransmitted ack or window probe.  Send it uncompressed
                 * in case the other side missed the compressed version.
                 */
                if (ip->ip_len != cs->cs_ip.ip_len &&
                                ntohs(cs->cs_ip.ip_len) == hlen)
                        break;

                /* (fall through) */

        case SPECIAL_I:
        case SPECIAL_D:
                /*
                 * actual changes match one of our special case encodings --
                 * send packet uncompressed.
                 */
                goto uncompressed;

        case NEW_S|NEW_A:
                if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
                        /* special case for echoed terminal traffic */
                        changes = SPECIAL_I;
                        cp = new_seq;
                }
                break;

        case NEW_S:
                if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
                        /* special case for data xfer */
                        changes = SPECIAL_D;
                        cp = new_seq;
                }
                break;
        }

        deltaS = (u_short)(ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id));
        if (deltaS != 1)
        {
                ENCODEZ(deltaS);
                changes |= NEW_I;
        }
        if (th->th_flags & TCP_PSH)
                changes |= TCP_PUSH_BIT;
        /*
         * Grab the cksum before we overwrite it below.  Then update our
         * state with this packet's header.
         */
        deltaA = ntohs(th->th_sum);
        BCOPY(ip, &cs->cs_ip, hlen);

        /*
         * We want to use the original packet as our compressed packet.
         * (cp - new_seq) is the number of bytes we need for compressed
         * sequence numbers.  In addition we need one byte for the change
         * mask, one for the connection id and two for the tcp checksum.
         * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
         * many bytes of the original packet to toss so subtract the two to
         * get the new packet size.
         */
        deltaS = (u_short)(cp - new_seq);
        if (!comp->compressSlot || comp->last_xmit != cs->cs_id)
        {
                comp->last_xmit = cs->cs_id;
                hlen -= deltaS + 4;
                pbuf_header(pb, -hlen);
                cp = (u_char *)pb->payload;
                *cp++ = changes | NEW_C;
                *cp++ = cs->cs_id;
        } else
        {
                hlen -= deltaS + 3;
                pbuf_header(pb, -hlen);
                cp = (u_char *)pb->payload;
                *cp++ = changes;
        }
        *cp++ = deltaA >> 8;
        *cp++ = deltaA;
        BCOPY(new_seq, cp, deltaS);
        INCR(vjs_compressed);
        return (TYPE_COMPRESSED_TCP);

        /*
         * Update connection state cs & send uncompressed packet (that is,
         * a regular ip/tcp packet but with the 'conversation id' we hope
         * to use on future compressed packets in the protocol field).
         */
uncompressed:
        BCOPY(ip, &cs->cs_ip, hlen);
        ip->ip_p = cs->cs_id;
        comp->last_xmit = cs->cs_id;
        return (TYPE_UNCOMPRESSED_TCP);
}

/*
 * Called when we may have missed a packet.
 */
void vj_uncompress_err(struct vjcompress *comp)
{
        comp->flags |= VJF_TOSS;
        INCR(vjs_errorin);
}

/*
 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
 * Return 0 on success, -1 on failure.
 */
int vj_uncompress_uncomp(
        struct pbuf *nb,
        struct vjcompress *comp
)
{
        register u_int hlen;
        register struct cstate *cs;
        register struct ip *ip;

        ip = (struct ip *)nb->payload;
        hlen = getip_hl(*ip) << 2;
        if (ip->ip_p >= MAX_SLOTS
                        || hlen + sizeof(struct tcphdr) > nb->len
                        || (hlen += getth_off(*((struct tcphdr *)&((char *)ip)[hlen])) << 2)
                        > nb->len
                        || hlen > MAX_HDR)
        {
                PPPDEBUG((LOG_INFO, "vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
                          ip->ip_p, hlen, nb->len));
                comp->flags |= VJF_TOSS;
                INCR(vjs_errorin);
                return -1;
        }
        cs = &comp->rstate[comp->last_recv = ip->ip_p];
        comp->flags &=~ VJF_TOSS;
        ip->ip_p = IPPROTO_TCP;
        BCOPY(ip, &cs->cs_ip, hlen);
        cs->cs_hlen = hlen;
        INCR(vjs_uncompressedin);
        return 0;
}

/*
 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
 * The packet is composed of a buffer chain and the first buffer
 * must contain an accurate chain length.
 * The first buffer must include the entire compressed TCP/IP header.
 * This procedure replaces the compressed header with the uncompressed
 * header and returns the length of the VJ header.
 */
int vj_uncompress_tcp(
        struct pbuf **nb,
        struct vjcompress *comp
)
{
        u_char *cp;
        struct tcphdr *th;
        struct cstate *cs;
        u_short *bp;
        struct pbuf *n0 = *nb;
        u32_t tmp;
        u_int vjlen, hlen, changes;

        INCR(vjs_compressedin);
        cp = (u_char *)n0->payload;
        changes = *cp++;
        if (changes & NEW_C)
        {
                /*
                 * Make sure the state index is in range, then grab the state.
                 * If we have a good state index, clear the 'discard' flag. 
                 */
                if (*cp >= MAX_SLOTS) {
                        PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: bad cid=%d\n", *cp));
                        goto bad;
                }

                comp->flags &=~ VJF_TOSS;
                comp->last_recv = *cp++;
        } else
        {
                /*
                 * this packet has an implicit state index.  If we've
                 * had a line error since the last time we got an
                 * explicit state index, we have to toss the packet. 
                 */
                if (comp->flags & VJF_TOSS) {
                        PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: tossing\n"));
                        INCR(vjs_tossed);
                        return (-1);
                }
        }
        cs = &comp->rstate[comp->last_recv];
        hlen = getip_hl(cs->cs_ip) << 2;
        th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
        th->th_sum = htons((*cp << 8) | cp[1]);
        cp += 2;
        if (changes & TCP_PUSH_BIT)
                th->th_flags |= TCP_PSH;
        else
                th->th_flags &=~ TCP_PSH;

        switch (changes & SPECIALS_MASK)
        {
        case SPECIAL_I: {
                register u32_t i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
                /* some compilers can't nest inline assembler.. */
                tmp = ntohl(th->th_ack) + i;
                th->th_ack = htonl(tmp);
                tmp = ntohl(th->th_seq) + i;
                th->th_seq = htonl(tmp);
        }
        break;

        case SPECIAL_D:
                /* some compilers can't nest inline assembler.. */
                tmp = ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
                th->th_seq = htonl(tmp);
                break;

        default:
                if (changes & NEW_U) {
                        th->th_flags |= TCP_URG;
                        DECODEU(th->th_urp);
                } else
                        th->th_flags &=~ TCP_URG;
                if (changes & NEW_W)
                        DECODES(th->th_win);
                if (changes & NEW_A)
                        DECODEL(th->th_ack);
                if (changes & NEW_S)
                        DECODEL(th->th_seq);
                break;
        }
        if (changes & NEW_I)
        {
                DECODES(cs->cs_ip.ip_id);
        } else
        {
                cs->cs_ip.ip_id = ntohs(cs->cs_ip.ip_id) + 1;
                cs->cs_ip.ip_id = htons(cs->cs_ip.ip_id);
        }

        /*
         * At this point, cp points to the first byte of data in the
         * packet.  Fill in the IP total length and update the IP
         * header checksum.
         */
        vjlen = (u_short)(cp - (u_char*)n0->payload);
        if (n0->len < vjlen)
        {
                /*
                 * We must have dropped some characters (crc should detect
                 * this but the old slip framing won't) 
                 */
                PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: head buffer %d too short %d\n",
                          n0->len, vjlen));
                goto bad;
        }

#if BYTE_ORDER == LITTLE_ENDIAN
        tmp = n0->tot_len - vjlen + cs->cs_hlen;
        cs->cs_ip.ip_len = htons(tmp);
#else
        cs->cs_ip.ip_len = htons(n0->tot_len - vjlen + cs->cs_hlen);
#endif

        /* recompute the ip header checksum */
        bp = (u_short *) &cs->cs_ip;
        cs->cs_ip.ip_sum = 0;
        for (tmp = 0; hlen > 0; hlen -= 2)
                tmp += *bp++;
        tmp = (tmp & 0xffff) + (tmp >> 16);
        tmp = (tmp & 0xffff) + (tmp >> 16);
        cs->cs_ip.ip_sum = (u_short)(~tmp);

        /* Remove the compressed header and prepend the uncompressed header. */
        pbuf_header(n0, -vjlen);

        if (MEM_ALIGN(n0->payload) != n0->payload)
        {
                struct pbuf *np, *q;
                u8_t *bufptr;

                np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
                if (!np) {
                        PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: realign failed\n"));
                        *nb = NULL;
                        goto bad;
                }

                pbuf_header(np, -cs->cs_hlen);

                bufptr = n0->payload;
                for (q = np; q != NULL; q = q->next) {
                        memcpy(q->payload, bufptr, q->len);
                        bufptr += q->len;
                }

                if (n0->next) {
                        pbuf_chain(np, n0->next);
                        pbuf_dechain(n0);
                }
                pbuf_free(n0);
                n0 = np;
        }

        if (pbuf_header(n0, cs->cs_hlen))
        {
                struct pbuf *np;

                LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
                np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
                if (!np) {
                        PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: prepend failed\n"));
                        *nb = NULL;
                        goto bad;
                }
                pbuf_cat(np, n0);
                n0 = np;
        }
        LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
        memcpy(n0->payload, &cs->cs_ip, cs->cs_hlen);

        *nb = n0;

        return vjlen;

bad:
        comp->flags |= VJF_TOSS;
        INCR(vjs_errorin);
        return (-1);
}

#endif


